Projectiles for rifle and handgun ammunition (bullets) are often designed with hollow or soft points or polymer-filled tips that allow the projectile to expand in diameter upon impact with a soft tissue target. Specific design of the projectile allows control of its expansion such that the projectile penetrates sufficiently to hit vital organs, yet is still retained by and comes to rest within the target. Bullet retention is thought to allow all its kinetic energy to be deposited within target, further enhancing its lethality. Even when the bullet does not come to rest within the target, if expansion dramatically slows the bullet, sufficient kinetic energy may be deposited to the soft tissue to also increase lethality.
While such considerations have been important to the theory and practice of bullet design, they are not readily applicable to designing spherical projectiles such as birdshot or buckshot. For example, bullets will consistently impact the target with the nose or tip hitting the target first, and bullet designs are based on this certainty. Spherical projectiles may hit the target without predictability in which leading portion of the projectile will encounter the target first. Moreover when multiple shot projectiles are loaded into shotshells, they are typically or often loaded in random orientations. Therefore, applying conventional bullet design considerations to improving spherical projectile performance becomes an insurmountable problem.
What is needed is a design that allows generally spherical projectiles such as shot to controllably expand in effective diameter when striking soft tissue. Such a design would be applicable regardless of the size of the shot, so that even large buckshot would still have a high likelihood of being retained within the soft tissue target for energy deposit.